Epoxy post cure

[rpmag]

Will the epoxy resin used in an adhesive such as JB Weld benefit from an elevated post cure as other epoxy resin systems reportedly do? and if yes will it improve the actual adhesion properties as well as the general performance?
BTW JB Weld themselves have not yet answered this question.

 

[Goahead]

May I suggest that the properties looked for should be defined more precisely.

At least three different test procedures were defined by ASTM, implying that the properties looked for may be different for different applications.
See:

ASTM D1002-01
Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal)

ASTM D1876-01
Standard Test Method for Peel Resistance of Adhesives (T-Peel Test)

ASTM C633-01
Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings
Note: this last test includes a calibration test to find the minimum properties of the adhesive, without any spray coating. This bond test is done by pulling normally to the bonded surface.

Any eventual benefit looked for in an adhesive should be tested in a way meaningful for the intended applications.

http://www.welding-advisers.com/

 

[rpmag]

Yes I see your point and I also see that I have not been clear enough.
The Epoxy in this application is used as a filler material within the intake port of an petrol IC engine, rather than a bonding agent. As such it is subject to temperature fluctuations from 0-100 deg c, which is well within the proposed temperature range for the epoxies used (according to manufacturers information).
However the often stated objections to the use of such material is that it will not survive the repeated temperature variations and the washing action of the fuels. Naturally the failure of the material can be catastrophic.
The thoughts of a post cure was to increase the material properties cf adhesion and temperature resistance.

 

[unclesyd]

With most epoxies the adhesive properties are set when the material is applied and cannot be improved by heating and in fact with some an increase in temperature is detrimental to the adhesion. One of the problems with adhesion such as your case is the differential expansion of the metal and the epoxy.
There are many consideration in situations as you describe and as you state failure can cause catastrophic results. One thing that is used in similar cases is to use a filled epoxy to enhance the properties of the buildup. They are several I've seen for use in your exact situation.

If you want a higher performance material a good company to talk to is Master Bond.

http://www.masterbond.com

 

[rpmag]

Thank you for your reply. Yes the expansion issues are often quoted and will remain a problem, do you feel that a filled epoxy will perform better?
In my way of thinking if the epoxy fails during the post cure to say 50deg C for 3 hours, then it would fail in use, as the cylinder head would easily surpass this temperature in operation. Similarly if it degrades then it is not really suitable for the job.
The filled epoxy I am familiar with are the loctite products and JB Weld, I will have a look at the masterbond

 

[BillPSU]

You may want to look at some Devcon products especially Wear Guard High Temp 450.

http://www.devcon.com/devconfamilyproduct.cfm?familyid=119.0&catid=34

 

[rpmag]

Thanks for that link, it is very helpful. The range of products is very good and the one you mentioned seems great for the job.
I will contact Devcon and get specific advice.

 

[rpmag]

News from the companies is mixed. Information supplied from JB Weld suggested that post cure may reduce the performance of the epoxy and it may fail, which is a curious thing given the temp rating of the cured adhesive is 200% of the suggested post cure temp.
Devcon noted that some of their products need a post cure to attain performance and all of their epoxy resins would most probably gain in performance from a post cure.
Two other well know suppliers did not return calls or emails.